Clutch plate members of the type described in the present invention are used extensively in automotive transmissions utilizing a fluid medium. When used in an automotive transmission as the driving member, a clutch plate member compresses and engages a driven member to drive the vehicle when pressure is applied to it. To increase the fuel economy of a vehicle, it is desirable to have the clutch plate members engaged over a wide range of slip speed (engine and transmission speed differential). It is therefore an important consideration when designing a clutch plate member to use a friction material which can be efficiently operated at a lower operating temperature over a wide range of slip speed. This lower operating temperature leads to a more durable clutch plate member having a longer service life.
Another important consideration in the design of a clutch plate member is that the frictional property of the material should remain approximately constant over the wide range of slip speed that the clutch plate member operates in order to minimize the transmission shudder phenomenon. Transmission shudder usually occurs at the friction interface where the static or low speed coefficient of friction is higher than the dynamic or high speed coefficient of friction. This condition causes the clutch to operate in a so-called stick slip mode which in turn translates into the transmission shudder phenomenon.
A variety of friction materials have been used to construct the friction facing layer of an automotive clutch plate member. Most of these traditional friction materials can be categorized into two types. The first type is a highly porous fibrous material made first by traditional paper making technology and then saturated with a thermoset plastic binder such as phenolic or epoxy. This type of material provides good conformability with a rigid mating surface due to its high compressibility. However, they typically have only a medium internal strength and a medium heat resistance therefore limiting their use to medium duty transmission applications. Materials of this type are described in U.S. Pat. No. 3,316,138 to Taylor and Almen et al U.S. Pat. No. 2,733,797, both assigned to the assignee of the present invention.
The second traditional type of friction material is a highly rigid material composed of grannular or fibrous carbon or other similar materials bonded together by a thermoset type of plastic resin or a metallic brazing material. These materials have very high internal strength and high energy absorbing capacity. However, they have the inherent drawback of poor conformability to a mating surface due to their rigidity. This poor conformability leads to hot spot formation in the friction material which in turn causes higher overall operating temperature of the clutch plate member. It is believed that higher operating temperatures cause premature failure of the friction facing layer and consequently a short service life. Materials of this type are disclosed in Yamamoto et al U.S. Pat. No. 4,146,527 and German Patent Application No. 1-525-334.
It is therefore an object of the present invention to provide a clutch plate member having a friction facing layer that offers both the conformability of a porous fibrous material and the strength and energy absorbing capacity of a hard grannular material.
It is another object of the present invention to provide a clutch plate member having a friction facing layer of high conformability, high strength, and energy absorbing capacity, and can be manufactured in a continuous process at low cost.